The present invention relates to a molding apparatus for die casting, which is provided with an improved degassing mechanism for allowing gas inside a cavity of a mold to be smoothly exhausted therefrom.
It has been known that a degassing groove is formed in a mold for exhausting air or gas from a cavity inside the mold when a molten material is supplied to the die for die casting. After the molten material is filled in the cavity, the degassing groove is closed by the molten material, and the molten material in the die is cooled.
FIG. 1 shows a conventional die casting apparatus 10, which is formed of a fixed die 11 and a movable die 12. The fixed die 11 includes a sleeve 13 with a piston 14, by which a molten material is supplied inside the apparatus 10. The movable die 12 includes a sprue runner 15 and a cavity 16, which is communicated with the atmosphere through an outlet 17, a concave 18 and a degassing portion 19.
In one example, the degassing portion 19 has a height of 0.05-0.25 mm with respect to the fixed die 11, a width of 10-40 mm, and a length of about 100 mm between the concave 18 and an outside of the die 12. The degassing portion 19 may be tapered outwardly such that a height relative to the fixed die 11 at a side of the concave 18 is the largest.
When the apparatus 10 is used, the movable die 12 is attached to the fixed die 11, and a molten material is supplied to the sleeve 13. As the piston 14 is moved forwardly, the molten material is supplied to the cavity 16 through the sprue runner 15, while air or gas inside the cavity 16 is exhausted through the outlet 17, the concave 18 and the degassing portion 19. After the cavity 16 is filled with the molten material, the molten material enters into the outlet 17, the concave 18 and the degassing portion 19, and is solidified thereat.
When the molten material enters into the outlet 17, however, since the outlet 17 is wide, the molten material does not flow linearly. The molten material flows obliquely or freely in the outlet 17, and as a leading portion of the molten material reaches a forward end of the degassing portion 19, the molten material solidifies thereat in order.
As the molten material does not arrive instantaneously along the entire width of the forward end of the degassing portion 19, the molten material solidifies partly at the forward end of the degassing portion 19. Therefore, the molten material subsequently supplied or arrived at the degassing portion 19 flows to portions where there is no hardened material. Namely, it causes partial flow or unbalanced flow of the molten material. Further, the molten material may partly blow up from the degassing portion 19.
In order to obviate these problems, the conventional molding apparatus has been formed such that the degassing portion 19 is made to have a small height of about 0.1 mm, and a long length of about 100 mm.
In the molding apparatus, lubricating oil is generally applied inside the sleeve 13 in order to prevent burning of the piston 14 inside the sleeve 13. When the degassing portion 19 is formed as explained above, the oil may cause another problem.
Namely, when the molten material is supplied to the sleeve 13, the lubricating oil evaporates by heat, i.e. about 700.degree. C., of the molten material, and the evaporated oil flows outwardly through the degassing portion 19. However, the temperature at the degassing portion 19 is low, i.e. about 200.degree. C., and the degassing portion 19 is very narrow in height and long in length. Therefore, while the evaporated oil flows through the degassing portion 19, the evaporated oil is condensed thereat and becomes oil with high stickiness. Also, a part of the evaporated oil adheres to the inside of the cavity.
As a result, the degassing portion 19 is clogged by the condensed oil. Since the degassing portion 19 is very small in height, even if pressure of 500 kg/cm.sup.2 is applied from the inside of the mold 10, the clogged oil may not be blown up from the degassing portion 19.
In the conventional apparatus, while the degassing portion 19 is clogged by oil, the molten material is supplied to the cavity 16. Therefore, high temperature and pressure are applied to the lubricating oil adhered to the surface of the cavity 16.
As a result, the oil in the cavity 16 is decomposed to form a large amount of hydrogen and carbon. Namely, hydrogen gas is formed inside the cavity 16, which is mixed with the molten material to form pores, swelling and so on. Also, carbon formed by decomposition of oil makes the product black.
The present invention has been made in view of the above drawbacks and to solve the problems.
Accordingly, one object of the present invention is to provide a molding apparatus, which can easily make a molding product without pores, swelling and so on.
Another object of the invention is to provide a molding apparatus as stated above, wherein flow of a molten material is properly regulated.
A further object of the invention is to provide a molding apparatus as stated above, wherein the size of the apparatus is made compact.
A still further object of the invention is to provide a molding apparatus as stated above, which can be formed easily and economically without substantial change of the conventional apparatus.
Further objects and advantages of the invention will be apparent from the following description of the invention.